Smoke detector

ABSTRACT

To enable an air velocity of sampling air to be precisely measured, a smoke detector (S) includes: a smoke detection part ( 22 ) connected to a sampling pipe ( 11 ); a fan ( 12 ) that sucks sampling air (SA) into the sampling pipe; and an air velocity sensor ( 15 ) that measures an air velocity of the sampling air within the sampling pipe. The air velocity sensor ( 15 ) is disposed at a primary side of the fan ( 12 ), and a straightening vane ( 25 ) is disposed between the air velocity sensor ( 15 ) and a suction port ( 12   a ) of the fan ( 12 ).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a smoke detector that optically detectsa contaminant such as smoke caused by fire and floating in the air, anddetects the fire.

2. Description of the Related Art

A smoke detector is used for preventing fire or as a detecting system ata time of generation of the smoke or in a semiconductor manufacturingplant or a food factory requiring a certain level of environmentalconservation.

The conventional smoke detector includes a smoke detection partconnected to a sampling pipe, a fan that sucks sampling air into thesampling pipe, and a wind velocity sensor that measures a wind velocityof the sampling air within the sampling pipe (for example, refer to JP3714926 B).

In the smoke detector, the sampling air flowing within the sampling pipeis partially introduced into the smoke detection part, and smokedetection is executed by a smoke sensor of the smoke detection part.After that, the sampling air is returned into the sampling air pipe. Atthis time, the fan is controlled on the basis of the air velocitymeasured by the air velocity sensor, and so controlled as to supply thesampling air as designed to the smoke detection part.

Further, the conventional smoke detector includes a smoke detection parthaving an inflow port and an outflow port, a sampling pipe disposed in amonitor space, an airflow pipe in which the sampling air flows, anintake side flow path branch part disposed in the airflow pipe andcoupled to the inflow port of the smoke detection part, and a filterdisposed between the inflow port and the intake side flow path branchpart (for example, refer to JP 2000-509535 A).

In the smoke detector, a part of the sampling air flowing within theairflow pipe is introduced from an inlet of the intake side flow pathbranch part, and supplied to the smoke detection part after dust or thelike are removed by the filter. Then, after smoke detection is executedby the smoke sensor of the smoke detection part, the sampling air isreturned into the airflow pipe from the outflow port through an exhaustside flow path merging part.

As illustrated in FIG. 4, a fan 2 is incorporated into a sampling pipe1, and an opening part 3 that sucks sampling air SA is defined at oneend thereof.

When the fan (blower fan) 2 is used with a high air volume, an openingpart 3 a (sampling air intake) is opened large as indicated by a phantomchain line, and no disturbance of airflow which induces a reverse flowin a primary side pipe of the fan occurs in the vicinity of a suctionport 4 of the fan 2.

However, when the opening part 3 a is made smaller to reduce the suctionair volume, the disturbance of airflow occurs within the primary sidepipe of the fan due to rotation of rotor blades within the fan 2, andthe reverse flow starts.

When the opening part 3 a is further made as small as the opening part 3indicated by a phantom solid line to further reduce the suction airvolume, a reverse flow L circulates within the sampling pipe 1 due tothe disturbance of air flow from the fan 2, and passes through an airvelocity sensor 5. This makes the flow unstable in the vicinity of theair velocity sensor 5, and hence the air velocity cannot be preciselymeasured.

Therefore, in order to solve the above-mentioned problem, it isconceivable to sufficiently separate the air velocity sensor 5 apartfrom the fan 2 so as to avoid an influence of the reverse flow L, whichis however not preferable since the smoke detector is upsized.

SUMMARY OF THE INVENTION

In view of the above-mentioned circumstance, a first object of thepresent invention is to enable the air velocity of the sampling air tobe precisely measured.

Further, in the conventional example, a part of the sampling aircontaining dust or the like is directly introduced into the airflowpipe, and passes through the filter, and hence there is a case in whicha large amount of dust or the like is deposited on the filter, or thefilter is clogged with the dust. For that reason, the filter must befrequently cleaned or replaced, and hence it takes much time and expenseto conduct maintenance work of the filter.

In view of the above-mentioned circumstance, a second object of thepresent invention is to reduce the amount of foreign matter such as dustwhich is sucked from an intake port of the intake side flow path branchpart.

In the conventional smoke detection system, an inlet manifold isconnected to the suction port of the fan. The fan sucks air into theinlet manifold through a pipe. Air from the outlet of the fan isexhausted directly to the atmosphere or to an exhaust pipe through anexhaust line except for a very small portion used for the purpose ofsampling in the entire air flow that flows through the fan.

Then, a part of flow used for the purpose of sampling passes through thefilter and enters the inlet of a detection chamber of the smokedetector. The outlet of the detection chamber is connected to the inletmanifold. However, the opening of the connection portion has been small,and the pressure loss of a flow at the branch part for sampling has beenlarge.

In view of the above-mentioned circumstances, a third object of thepresent invention is to enable the pressure loss of the flow at thebranch part having the smoke detection part to be reduced, and thesampling air flow exhausted from the smoke detection part and thesampling air flow in the airflow pipe which is sucked by the fan to bestably merged.

According to a first aspect of the present invention, a smoke detectorincludes: a smoke detection part connected to a sampling pipe; a fanthat sucks sampling air into the sampling pipe; and an air velocitysensor that measures an air velocity of the sampling air within thesampling pipe, in which the air velocity sensor is disposed at a primaryside of the fan, and a straightening vane is disposed between the airvelocity sensor and a suction port of the fan.

According to a second aspect of the present invention, a smoke detectorincludes: a smoke detection part having an inflow port and an outflowport; a sampling pipe disposed in a monitor space; an airflow pipecoupled with the sampling pipe; and an intake side flow path branch partdisposed in the airflow pipe and coupled with the inflow port of thesmoke detection part, in which the intake side flow path branch part hasan intake port directed opposite to a flow direction of sampling airflowing in the airflow pipe.

According to a third aspect of the present invention, a smoke detectorincludes: a smoke detection part having an inflow port and an outflowport; a sampling pipe disposed in a monitor space; an airflow pipecoupled with the sampling pipe, in which a fan intervenes; a flow pathbranch part coupled with an inflow port of the smoke detection part; anda flow path merging part disposed in the airflow pipe and coupled withthe outflow port of the smoke detection part through an exhaust pipe, inwhich the flow path merging part is equipped with a nozzle part havingan opening larger than the exhaust pipe, which sprays air toward a venthole lower in pressure than the flow path branch part of the fan.

According to the present invention, the air velocity sensor is disposedat the primary side of the fan, and the straightening vane is disposedbetween the air velocity sensor and the fan. Therefore, the reserve flowgenerated by the fan is blocked by the straightening vane, and cannotmove to the air velocity sensor side. For that reason, the flow isstable in the vicinity of the air velocity sensor without occurrence ofthe disturbance in a flow of fluid, and hence it is possible toaccurately measure the air velocity.

According to the present invention, the intake port of the intake sideflow path branch part is directed opposite to a flow direction of thesampling air that flows in the airflow pipe. For example, particlesheavier than smoke particles, such as dust, are advanced downstream inthe vicinity of the intake port due to an inertia force in a flowdirection of the sampling air because the flow direction cannot bechanged rapidly. For that reason, the dust or the like, sucked mixedlywith the sampling air, which is sucked from the intake port is verysmall in amount, and hence it is possible to remarkably reduce thenumber of cleaning or exchanging of the filter as compared with that inthe conventional art.

With the present invention being configured as described above, a partof the sampling air flowing in the airflow pipe is introduced into thesmoke detection part due to a pressure difference occurring between theflow path branch part and the flow path merging part, and returns to theairflow pipe from the flow path merging part through the smoke detectionpart.

In this case, the sampling air exhausted from the smoke detection partthrough the exhaust pipe is merged through the flow path merging parthaving a nozzle part with an opening larger than the exhaust pipe, whichsprays air that is substantially uniformly spread toward a vent holelower in pressure than the flow path branch part of the fan.

Accordingly, the pressure loss of the flow at the branch part having thesmoke detection part can be reduced, and hence the flow rate of thebranch part flow can be increased. Further, the sampling air flowexhausted from the smoke detection part and the sampling air flow suckedby the fan can be stably merged.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is an enlarged perspective view illustrating a first embodimentof the first invention;

FIG. 2 is a configuration diagram illustrating the first embodiment ofthe first invention;

FIG. 3 is a plan view illustrating a second embodiment of the firstinvention;

FIG. 4 is an enlarged perspective view illustrating a conventionalexample of the first invention;

FIG. 5 is a plan view illustrating a third embodiment of the presentinvention;

FIG. 6 is an enlarged cross-sectional view illustrating a main portionof FIG. 5;

FIG. 7 is a cross-sectional view of an intake side flow path branch part133 taken along a line III-III;

FIG. 8 is a front enlarged cross-sectional view illustrating a fourthembodiment of the present invention and corresponding to FIG. 6;

FIG. 9 is an explanatory diagram illustrating a main portion of a smokedetector according to the present invention; and

FIG. 10A is a perspective view illustrating a nozzle used in the presentinvention, and FIG. 10B is a perspective view of an extended nozzle ofFIG. 10A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention is described with referenceto FIGS. 1 and 2.

A smoke detector S includes a smoke detection part 22 connected to asampling pipe 11 through a pipe 20, a filter 23 disposed at an inflowport 22 a side of the smoke detection part 22, a fan (blower fan) 12that sucks sampling air SA into the sampling pipe 11, and an airvelocity sensor (flow sensor) 15 that measures an air velocity of thesampling air SA within the sampling pipe 11.

The smoke detection part 22 is provided with a light receiving element(smoke sensor) (not shown) such as a light emitting element and aphotodiode, a light trap (not shown), a condenser lens (not shown), anaperture (not shown), and so on.

Within an inflow part 40 having a substantially box shape, and an intakeport (not shown) for the sampling air arranged at a side surface thereofand a suction port 12 a of the fan 12 arranged at a bottom surfacethereof, an airflow direction of the sampling air SA at a primary sideof the fan 12 is substantially orthogonal to an airflow direction SBcaused by the suction port 12 a of the fan 12. A straightening vane 25is disposed between the primary side (upstream side) of the fan 12 andthe air velocity sensor 15. The straightening vane 25 is formed into asubstantially rectangular configuration (for example, about 50 mm inwidth and about 10 mm in height), and disposed at an angle α (forexample, about 90°) to the bottom surface, and an angle θ (for example,about 90°) to the airflow direction of the sampling air SA. The inventorof the present invention has conducted comparative experiments between acase in which the straightening vane 25 is disposed within the inflowpart 40 as illustrated in FIG. 1, and a case in which the straighteningvane 25 is not disposed. Then, the inventor of the present invention hasconfirmed that, when the straightening vane 25 is arranged, outputs ofthe air velocity sensor 15 have a proportional relationship from a lowair volume to a high air volume. That is, the straightening vane 25 ismeans for preventing a reverse flow L occurring due to a reduction inthe air volume sucked by the fan 12 from moving to the air velocitysensor 15 side. The angles α and θ of the straightening vane 25 are setto be within a range of about 45 to 90° according to the fan 12 in orderto prevent the reverse flow from the suction port 12 a of the fan 12from affecting the flow velocity measurement.

The configuration of the straightening vane 25 may be square or triangleother than substantially rectangle, and its size or the like isappropriately selected in a range where the function thereof can beexerted.

Further, the straightening vane 25 may be disposed on, for example, aceiling surface or the like other than the bottom surface, and also thestraightening vanes 25 may be disposed at a plurality of locations onboth of the bottom surface and the ceiling surface. Further, the airvelocity sensor 15 and the suction port 12 a can be arranged immediatelyclose to both sides of the straightening vane 25 (for example, about 30mm or lower), and hence the inflow part 40 can be sufficientlydownsized.

Next, the operation of the first embodiment is described.

When the fan 12 is driven, air in a monitor space is sucked into thesampling pipe 11, and the sampling air SA flows in the sampling pipe 11.

In this situation, after the air velocity thereof is measured by the airvelocity sensor 15, the sampling air SA enters the fan 12 from thesuction port 12 a, and is exhausted from an exhaust port 12 b whilecircling. A part of the sampling air SA passes through the pipe 20 andthe filter 23, and enters the smoke detection part 22. Then, after smokedetection is executed by the smoke sensor (not shown) in the smokedetection part 22, the sampling air SA is returned to the sampling pipe11.

When the suction air volume is small (at the time of the low airvelocity), the reverse flow L occurs because the airflow in the pipe atthe primary side of the fan 12 is disturbed by rotation of rotor bladeswithin the fan 12. The reverse flow L is going to spread toward theupstream side within the sampling pipe 11, but collides with thestraightening vane 25 because the straightening vane 25 is disposed onthe upstream side. For that reason, the reverse flow L cannot reach thevicinity of the air velocity sensor 15, and hence no disturbance of thefluid flow occurs in the vicinity of the air velocity sensor 15, and theflow becomes stable, thereby enabling the air velocity to be preciselydetected. Accordingly, the fan 12 controlled on the basis of themeasurement value of the air velocity sensor 15 can be preciselycontrolled, and hence the sampling air as designed can be stablysupplied to the smoke detection part 22, thereby enabling smokedetection high in precision. Further, the air velocity sensor 15 and thesuction port 12 a can be disposed immediately close to the straighteningvane 25, thereby enabling sufficient downsizing.

A second embodiment of the present invention is described with referenceto FIG. 3, and the same reference symbols of those of FIGS. 1 and 2 arealso identical in the name and function.

A difference between the second embodiment and the first embodimentresides in that the straightening vane 25 is rotatably supported on thebottom surface or the ceiling surface of the inflow part 40 by a supportshaft p. With the above-mentioned configuration, the straightening vane25 can be set to the angle θ having the most shielding effect withrespect to the reverse flow L according to the rotation speed of the fan12 or the output of the air velocity sensor 15, and hence smokedetection with high precision can be executed even when the air velocityfrequently varies.

A third embodiment according to the second invention is described withreference to FIGS. 5 and 6.

As illustrated in FIG. 5, a smoke detector 101 includes a smokedetection unit 102 having a dark box 121, a fan 103 that feeds air(sampling air) SA to be detected to the smoke detection unit 102, a pipe104 serving as an air passage, a light emitting element 111 disposedwithin the smoke detection unit 102, a light receiving element 112 suchas a photodiode, an air flow sensor 113 that measures the flow rate ofthe air and the fan 103, a power supply part 114 that supplies a powerto the air flow sensor 113, and a fire determination part 115 connectedto the light receiving element 112.

A smoke detection part 125 is disposed in the center of the dark box 121of the smoke detection unit 102, and the sampling air SA that has passedthrough the pipe 104 and filtered by the filter 105 is introduced intothe smoke detection part 125. Reference numeral 123 denotes a light trapdisposed in a light shielding part 122, reference numeral 124 denotes acondenser lens, and reference numeral 126 denotes an aperture.

The fire determination part 115 includes an amplifier circuit thatamplifies an output signal S of the light receiving element 112, an A/Dconverter that converts a level of the amplifier circuit into adetection level, a comparator circuit that determines that fire occurswhen the detection level becomes equal to or higher than a predeterminedthreshold value, and so on. The comprehensive control is executed by aCPU.

A diffuser part 120 is disposed at the secondary side of the fan 103 inan airflow pipe P. The diffuser part 120 spreads toward the downstreamside. For example, the diffuser part 120 is of a divergent pipe(diffuser) forming substantially a cone such as a circular cone, anexhaust side flow path merging part 132 is disposed at a base end part120 a side, and an intake side flow path branch part 133 is disposed ata leading end part 120 b side.

An intake port 133 a of the intake side flow path branch part 133 isformed at the leading end part of a projection pipe 133P bent in anL-shape, and the leading end part of the projection pipe 133 p isreserve to a flow direction C of the sampling air SA flowing in theairflow pipe P (is directed downstream). Further, an exhaust port 132 aof the exhaust side flow path merging part 132 is formed at a leadingend part of a projection pipe 132P bent in an L-shape, and the leadingend part of the projection pipe 132 p is directed opposite to the flowdirection C of the sampling air SA flowing in the airflow pipe P (isdirected downstream). Accordingly, the intake port 133 a and the exhaustport 132 a are directed in the same direction.

At the secondary side of the fan 103, the dark box 121 of the smokedetection unit 102 is provided, and an inflow port 133 c of the smokedetection part 125 in the dark box 121 is connected to the intake port133 a of the intake side flow path branch part 133 through the filter105, and an outflow port 132 c thereof is connected to the exhaust port132 a of the exhaust side flow path merging part 132.

Next, the operation of a third embodiment is described.

When the fan 103 is driven, air A in the monitor space is sucked intothe airflow pipe P through the sampling pipe (not shown), and thenexhausted through the diffuser part 120. However, in this situation, theflow velocity in the exhaust side flow path merging part 132 within thediffuser part 120 is different from the flow velocity in the intake sideflow path branch part 133 thereof, and thus a pressure differencebetween both of those parts occurs.

Due to the occurrence of the pressure difference, smoke particlescontained in the sampling air SA flowing in the diffuser part 120 aresucked from the intake port 133 a of the intake side flow path branchpart 133, and pass through the filter 105 and enter the inflow port 133c of the smoke detection part 125. The smoke particles are thenirradiated with a laser beam of the light emitting element 111 andadvance within the smoke detection part 125 while generating a scatteredlight, pass through the exhaust port 132 a of the exhaust side flow pathmerging part 132 from the outflow port 132 c, and are returned to theinterior of the diffuser part 120.

Powder dust or the like F is contained in the sampling air SA flowing inthe airflow pipe P, but the powder dust or the like F is heavier thanthe smoke particles, and hence the powder dust or the like F flows downwith a large inertia force in a current direction. For that reason, thepowder dust or the like F advances downstream within the airflow pipe 4,unlike the light smoke particles mixed with the sampling air SA suckedinto the intake port 133 a, and hence the sampling air SA that is not orhardly mixed with the powder dust or the like F can be introduced fromthe intake port 133 a. Accordingly, the powder dust or the like Fdeposited on the filter 105 is remarkably reduced as compared with theconventional example, and hence it is possible to reduce the number ofcleaning or exchanging the filter.

FIG. 7 is a cross-sectional view of the intake side flow path branchpart 133 taken along a line III-III.

The projection pipe P of the intake side flow path branch part 133 isformed in an L-shape, and the intake port 133 a disposed at the leadingend part thereof is directed downstream. The leading end part is notexactly opposite to the flow direction C of the sampling air SA(identical in axial center with the flow direction C), but is inclinedby an angle α, for example, 10°. The angle α is a foreign matterentrance prevention angle which is capable of preventing the foreignmatter such as the powder dust or the like F from being mixed together,and is appropriately selected within a range of angles β and γ, forexample, a range of 0 (identical with the above-mentioned direction C)to 45°.

A fourth embodiment of the second invention is described with referenceto FIG. 8. The same reference symbols as those of FIGS. 6 and 7 are alsoidentical in name and function.

Differences between the fourth embodiment and the third embodiment arestated below.

(1) As pressure difference generating means, the diffuser part 120 isreplaced with an orifice 136. The orifice 136 is disposed between theintake side flow path branch part 133 and the exhaust side flow pathmerging path 132 of the airflow pipe P.

(2) The intake side flow path branch part 133 is disposed not downstreamof the exhaust side flow path merging path 132, but upstream thereof.

In the fourth embodiment, it is difficult to change the flow directionof the powder dust or the like F from the main flow to the oppositedirection due to the inertia force thereof. For that reason, the mixtureof the powder dust or the like F into the intake port 133 a is reduced,and hence the filter lifetime can be extended as compared with theconventional example, and false detection of the fire determination partdue to the powder dust or the like F is also reduced.

A fifth embodiment of the third invention is described with reference tothe drawings on the basis of an example.

FIG. 9 illustrates a smoke detector according to the example of thepresent invention, in which a smoke detector 201 is designed such thatan airflow pipe 202 is connected to a sampling pipe arranged in amonitor space (not shown), a fan 203 (for example, blower fan) thatsucks and exhausts contaminated air in the monitor space as the samplingair A is disposed to the upstream part (primary side) of the airflowpipe 202, and a flow path branch part 205 that allows a part of thesampling air A exhausted from the fan 203, that is, the sampling air SAto be detected, to flow into the smoke detection part 204 is formed inthe downstream part (secondary side) of the airflow pipe 202.

The flow path branch part 205 is connected with a sampling air inflowpipe 206 that circulates the sampling air SA to be detected, and one endof the sampling air inflow pipe 206 is connected to an inflow port 208of a smoke detection part 204 for the sampling air SA, which includes afilter 207 and a smoke detection unit made up of optical smoke detectingmeans having a light emitting element (not shown) and a light receivingelement (not shown), air flow rate measuring means, and so on.

On the other hand, an outflow port 209 of the smoke detection part 204for the sampling air SA is connected with one end of a sampling airexhaust pipe 210, and a flow path merging part at another end of thesampling air exhaust pipe 210 (for the sampling air which has passedthrough the smoke detection part 204) is connected to a vent hole 203 athat is lower in pressure than the flow path branch part immediatelyclose to the peripheral edge of the rotor blades of the fan 203.

A flow path merging part 211 includes the vent hole 203 a of the fan 203which has an opening larger than that of the sampling air exhaust pipe210, and a nozzle 212 having one end connected to the sampling airexhaust pipe 210, and another end with substantially the same opening asthat of the vent hole 203 a of the fan 203 and capable of spraying thesampling air SA with a flow that substantially uniformly spreads towardthe vent hole 203 a of the fan 203.

With the above-mentioned configuration, it is possible to reduce thepressure loss of a flow in the branch part including the smoke detectionpart 204, and to stably merge together the sampling air flow exhaustedfrom the smoke detection part 204 and the sampling air flow of theairflow pipe 202, which is sucked by the fan 203.

Further, an example of the nozzle 212 is described with reference toFIGS. 10A and 10B. At an opening end forming the flow path merging part211 disposed at the another end of the sampling air exhaust pipe 210(for the sampling air which has passed through the smoke detection part204) is disposed an outer cylinder 213 having substantially the sameopening W1 as the opening diameter of the vent hole 203 a of the fan203. The outer cylinder 213 is configured to be extendable asillustrated in FIG. 10B, whereby the size of the injection port of thenozzle 212 can be adjusted to an opening W2 larger than the opening ofthe vent hole 203 a of the fan 203.

In order to supply a stable and substantially uniform flow to the venthole 203 a, the leading end of the nozzle 212 may be configured to begradually spread.

In this example, an inner cylinder 214 extendable laterally may beincorporated into the outer cylinder 213, and a clamp 215 such as arivet is inserted into a clamp hole 216, thereby making it possible toprovide a given width for the opening W1 or W2.

The extendable nozzle is not limited to the above-mentioned example.

In FIG. 9, reference symbol P1 denotes an air inflow port, and referencesymbol P2 denotes an air exhaust port.

1. A smoke detector, comprising: a smoke detection part connected to asampling pipe; a fan that sucks sampling air into the sampling pipe; andan air velocity sensor that measures an air velocity of the sampling airwithin the sampling pipe, wherein the air velocity sensor is disposed ata primary side of the fan, and a straightening vane is disposed betweenthe air velocity sensor and a suction port of the fan.
 2. A smokedetector according to claim 1, further comprising an inflow part inwhich an airflow direction of the sampling air at the primary side ofthe fan and an airflow direction due to the suction port of the fan aresubstantially orthogonal to each other.
 3. A smoke detector according toclaim 2, wherein the straightening vane is rotatably supported on one ofa bottom surface and a ceiling surface of the inflow part.
 4. A smokedetector, comprising: a smoke detection part having an inflow port andan outflow port; a sampling pipe disposed in a monitor space; an airflowpipe coupled with the sampling pipe; and an intake side flow path branchpart disposed in the airflow pipe and coupled with the inflow port ofthe smoke detection part, wherein the intake side flow path branch parthas an intake port directed opposite to a flow direction of sampling airflowing in the airflow pipe.
 5. A smoke detector according to claim 4,wherein the intake port is directed opposite to the flow direction ofthe sampling air in a range of 0 to 45°.
 6. A smoke detector accordingto claim 4, wherein the intake port of the intake side flow path branchpart is disposed one of upstream and downstream of an exhaust port of anexhaust side flow path merging part.
 7. A smoke detector according toclaim 5, wherein the intake port of the intake side flow path branchpart is disposed one of upstream and downstream of an exhaust port of anexhaust side flow path merging part.
 8. A smoke detector, comprising: asmoke detection part having an inflow port and an outflow port; anairflow pipe coupled with a sampling pipe disposed in a monitor space,in which a fan intervenes; a flow path branch part coupled with aninflow port of the smoke detection part; and a flow path merging partdisposed in the airflow pipe and coupled with the outflow port of thesmoke detection part through an exhaust pipe, wherein the flow pathmerging part is equipped with a nozzle part having an opening largerthan the exhaust pipe, which sprays air toward a vent hole lower inpressure than the flow path branch part of the fan.
 9. A smoke detectoraccording to claim 8, wherein the opening of the nozzle part isadjustable.